SANAA, Yemen — Yemen was thrust back into the forefront of the international fight against terrorism yesterday when the United States and Britain evacuated embassy staff due to a threatened attack, a suspected US drone killed four alleged members of al Qaeda, and militants shot down a Yemeni army helicopter.

As Westerners flew out of the country, Yemeni authorities launched a wide investigation into the al Qaeda threat to multiple potential targets in the impoverished Arab nation.

Security officials said they believed the terror network was seeking retaliation for an Amerocan-backed military offensive that has dealt serious setbacks to its most active branch, including the death earlier this year of its No. 2 leader.

Meanwhile, President Obama said on the “Tonight Show” last night that the United States was not overreacting to the threat, and minimized Americans’ chances of getting killed in a terror attack.

“The odds of dying in a terrorist attack are a lot lower than they are of dying in a car accident, unfortunately,” Obama said